Method for reducing output data noise of semiconductor apparatus and semiconductor apparatus implementing the same

ABSTRACT

Provided is a semiconductor apparatus which includes a plurality of output buffers configured to connect a plurality of power sources, and a data noise measuring unit configured to fix an output data of a selected output buffer among the plurality of output buffers to have a specific level, measure a noise of the output data using a capacitance and control a slew rate of the plurality of output buffers based on the noise.

CROSS-REFERENCES TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.13/720,992 filed Dec. 19, 2012, the disclosure of which is incorporatedherein by reference.

BACKGROUND

1. Technical Field

The present invention generally relates to a semiconductor designtechnology, and more particularly, to a method for reducing output datanoise of a semiconductor apparatus and a semiconductor is apparatusimplementing the same.

2. Related Art

In general, a semiconductor apparatus includes an output buffer tooutput data. The output buffer drives high data from a power supplyvoltage, and drives low data from a ground voltage.

FIG. 1 is a circuit diagram illustrating a data output unit of aconventional semiconductor apparatus including a plurality of outputbuffers. The data output unit of the semiconductor apparatus includes anoutput buffer section 10. The output buffer section 10 includes aplurality of output buffers BUF0 to BUFn configured to receive dataD<0˜n> and output the received data D<0˜n> to input/output pads DQ<0˜n>.At this time, on-die termination (ODT) circuits may be connected to therespective input/output pads DQ<0˜n>, in order to compensate forimpedance matching of the output data Q<0˜n>.

The respective output buffers BUF0 to BUFn of the output buffer section10 drive high data from a power supply voltage VDDQ, and drive low datafrom a ground voltage VSSQ. Since the respective output buffers BUF0 toBUFn receive power from the common power sources VDDQ and VSSQ,simultaneous switching noise may occur in a power supply voltage VDDQ orground voltage VSSQ supplied to the output buffers BUF0 to BUFn when aplurality of data transit at the same time. For example, when aplurality of data transit to a high level to a low level, a largecurrent IL1 may be passed to the ground voltage source VSSQ, andsimultaneous switching noise VL1 may occur in the supplied groundvoltage VSSQ due to parasitic inductance L1 of the ground voltageterminal. The principle that the simultaneous switching noise VL1 occursmay be expressed by Equation 1 below.

$\begin{matrix}{V_{L_{1}} = {L_{1}\frac{\partial I_{L_{1}}}{\partial t}}} & \left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack\end{matrix}$

Furthermore, when a plurality of data transit from a low level to a highlevel, simultaneous switching noise VL2 may occur in the supplied powersupply voltage VDDQ due to parasitic inductance L2 of the power supplyvoltage terminal, based on the above-described principle.

The simultaneous switching noise may cause noise in the output dataQ<0˜n>.

FIG. 2 is a graph illustrating data noise which may occur in thesemiconductor apparatus of FIG. 1. FIG. 2 illustrates data noise whichmay occur when the plurality of output buffers drive output data Q<0:1>transiting from a high level to a low level. FIG. 2 also illustrates apower supply voltage VDDQ.

Low-level output data Q<k> is driven to a specific output buffer, andoutput data Q<0˜1> transiting from a high level (i.e., VOH) to a lowlevel (i.e., VOL) are driven to a plurality of output buffers. Since theplurality of output buffers change data from a high level to a lowlevel, large amounts of currents are passed to the ground voltage sourceVSSQ at the same time, and simultaneous switching noise VL1 occurs dueto parasitic inductance. Due to the influence of the simultaneousswitching noise VL1 occurring in the ground voltage VSSQ, data noiseoccurs in the output data Q<k> maintaining a low level.

Such output data noise does not guarantee the reliability of the entiresemiconductor apparatus.

SUMMARY

In an embodiment, there is provided a method for reducing output datanoise of a semiconductor apparatus which includes a plurality of outputbuffers to output data. The method includes the steps of: driving lowdata to a specific output buffer among the plurality of output buffers,and driving data transiting from a high level to a low level to theother output buffers; and measuring the magnitude of data noiseoccurring in output data of the specific output buffer, and decidingslew rates of the plurality of output buffers based on the measurementresult.

In an embodiment, there is provided a method for reducing output datanoise of a semiconductor apparatus which includes a plurality of outputbuffers to output data. The method includes the steps of: driving highdata to a specific output buffer among the plurality of output buffers,and driving data transiting from a low level to a high level to theother output buffers; and measuring a magnitude of data noise occurringin output data of the specific output buffer, and deciding slew rates ofthe plurality of output buffers based on the measurement result.

In an embodiment, a semiconductor apparatus includes: a plurality ofoutput buffers configured to be driven by a power supply voltage and aground voltage and output received data; and a data noise measuring unitconfigured to measure the magnitude of data noise from output data of aspecific output buffer among the plurality of output buffers, andgenerate a slew rate control signal to control slew rates of theplurality of output buffers based on the measurement result.

In an embodiment, a semiconductor apparatus includes: a plurality ofoutput buffers configured to electrically connect a plurality of powersources, and a data noise measuring unit configured to fix an outputdata of a selected output buffer among the plurality of output buffersto have a specific level, measure a noise of the output data using acapacitance and control a slew rate of the plurality of output buffersbased on the noise.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, aspects, and embodiments are described in conjunction with theattached drawings, in which:

FIG. 1 is a circuit diagram illustrating a data output unit of aconventional semiconductor apparatus including a plurality of outputbuffers;

FIG. 2 is a graph illustrating data noise which may occur in thesemiconductor apparatus of FIG. 1;

FIG. 3 is a flow chart showing a method for reducing output data noiseof a semiconductor apparatus according to an embodiment;

FIG. 4 is a flow chart showing a method for reducing output data noiseof a semiconductor apparatus according to an embodiment;

FIG. 5 is a diagram illustrating the configuration of a semiconductorapparatus implementing the method for reducing output data noiseaccording to an embodiment;

FIG. 6 is a circuit diagram illustrating an embodiment of an outputbuffer of FIG. 5;

FIGS. 7A and 7B are graphs illustrating an example of the operation ofthe semiconductor apparatus of FIG. 5; and

FIGS. 8A and 8B are graphs illustrating another example of the operationof the semiconductor apparatus of FIG. 5.

DETAILED DESCRIPTION

Hereinafter, a method for reducing output data noise of a semiconductorapparatus and a semiconductor apparatus implementing the same accordingto the embodiments will be to described below with reference to theaccompanying drawings through various embodiments.

FIG. 3 is a flow chart showing a method for reducing output data noiseof a semiconductor apparatus according to an embodiment.

The method for reducing output data noise, shown in FIG. 3, may widelybe applied to not only a data output unit of a semiconductor apparatuswhich outputs data to the outside, but also any parts of a semiconductorapparatus using output buffers.

In an embodiment, the method for removing output data noise may be usedto initially set output buffers during the initial setting of asemiconductor apparatus.

The method for removing output data noise of a semiconductor apparatusaccording to an embodiment measures the maximum data noise occurring inoutput buffers, and controls a slew rate of the output buffers based onthe magnitude of the data noise. As data noise increases, the influenceof simultaneous switching noise caused by parasitic inductance mayincrease. In this case, the amounts of currents flowing in a powersupply terminal at the same time during switching are reduced bydecreasing the slew rate.

Specifically, the maximum data noise occurring in output buffers ismeasured to remove output data noise of the semiconductor apparatusaccording to an embodiment. That is, low data is continuously driven toonly a specific output buffer of a plurality of output buffers, and datatransiting from a high level to a low level are driven to other outputbuffers at step S11. In order to to measure the maximum data noise, lowdata may be driven to only a specific output buffer. In this case, dueto the influence of the plurality of output buffers to change data to ahigh level to a low level, simultaneous switching noise occurs in thepower supply terminal. Due to the simultaneous switching noise, datanoise occurs in low data outputted from the specific output buffer.

Then, the magnitude of the data noise occurring in the output data ofthe specific output buffer is measured, and the slew rates of theplurality of output buffers are decided based on the measurement result.Specifically, this process includes a step S12 of measuring themagnitude of the data noise occurring in the output data of the specificoutput buffer and converting the measured magnitude into a digital codevalue and a step S13 of controlling the slew rates of the plurality ofoutput buffers based on the digital code value. During the step S13 ofcontrolling the slew rates of the plurality of output buffers based onthe digital code value, the slew rates of the entire output buffers maybe controller together, which is desirable in terms of designefficiency.

Specifically, the step S12 of measuring the magnitude of the data noiseoccurring in the output data of the specific output buffer andconverting the measured magnitude into a digital code value is performedas follows.

First, the data noise is amplified, and the magnitude of the amplifieddata noise is quantified by rectifying the amplified data noise at stepS12_2. That is, the magnitude of the amplified data noise is indicatedby a specific analog voltage level.

Then, the quantified magnitude of the amplified data noise is convertedinto the corresponding digital code value at step S12_3. For example,when the voltage level of the quantified data noise is higher than aspecific reference level, the digital code value may be set to reducethe slew rate of the output buffer. On the other hand, when the voltagelevel of the quantified data noise is lower than the specific referencelevel, the digital code value may be set to increase the slew rate ofthe output buffer.

At this time, considering a case in which the low-level output data ofthe specific output buffer is influenced by an ODT circuit or the likeso as to contain a DC component, the method may further include a stepS12_1 of removing a DC component of the output data and extracting an ACcomponent as the data noise.

In the step S13 of controlling the slew rates of the plurality of outputbuffers based on the digital code value, when the magnitude of the datanoise is larger than a reference value, the slew rates of the pluralityof output buffers are reduced in response to the digital code value.When the slew rates of the output buffers are reduced, it means that theoutput buffers reduce the amounts of currents driven at the same time.Therefore, the influence of simultaneous switching noise may be reduced,and thus data noise may be reduced.

On the other hand, when the magnitude of the data noise is smaller thanthe reference value, the slew rates of the plurality of to outputbuffers may be increased in response to the corresponding digital codevalue. This means that simultaneous switching noise does not have aneffect on the data output result. Therefore, the slew rates of theoutput buffers may be increased to a proper value for an efficientoperation of the output buffers.

FIG. 4 is a flow chart showing a method for reducing output data noiseof a semiconductor apparatus according to an embodiment.

The method for reducing output data noise, shown in FIG. 4, may beapplied to not only a data output unit of a semiconductor apparatuswhich outputs data to the outside, but also any parts of thesemiconductor apparatus using output buffers.

The method for reducing output data noise according to an embodiment maybe used to initially set output buffers during the initial setting of asemiconductor apparatus.

The method for reducing output data noise of a semiconductor apparatusaccording to an embodiment measures the maximum data noise occurring inthe output buffers, and adjusts the slew rates of the output buffersbased on the magnitude of the data noise. As the data noise increases,the influence of simultaneous switching noise caused by parasiticinductance may increase. In this case, the slew rates are reduced todecrease the amounts of currents flowing into the power supply terminalat the same time during switching.

Specifically, in order to reduce output data noise of the semiconductorapparatus according to an embodiment, the maximum data noise occurringin the output buffers is first measured. The method of FIG. 4 isdifferent from the method of FIG. 3 in that high data is continuouslydriven to only a specific output buffer of the plurality of outputbuffers, and data transiting from a low level to a high level are drivento the other output buffers at step S21. That is, the method of FIG. 3considers the maximum simultaneous switching noise occurring in theground voltage terminal, and the method of FIG. 4 considers the maximumsimultaneous switching noise occurring in the power supply voltageterminal. In order to measure the maximum data noise, high data may bedriven to only a specific output buffer. In this case, simultaneousswitching noise occurs in the power supply voltage terminal due to theinfluence of the plurality of output buffers changing data from a lowlevel to a high level. Due to the simultaneous switching noise, datanoise occurs in high data outputted from the specific output buffer.

Subsequent steps are performed in a similar manner to theabove-described embodiment of FIG. 3. That is, the magnitude of the datanoise occurring in the output data of the specific output buffer ismeasured, and the slew rates of the plurality of output buffers aredecided based on the measurement result. Specifically, the methodincludes a step S22 of measuring the magnitude of the data noiseoccurring in the output data of the specific output buffer andconverting the measured magnitude into a digital code value and a stepS23 of controlling the slew rates of the plurality of output buffersbased on the digital code value. During the step S23 of controlling theslew rates of the plurality of output buffers based on the digital codevalue, the slew rates of the entire output buffers may be adjustedtogether, which is desirable in terms of design efficiency.

Specifically, the step S22 of measuring the magnitude of the data noiseoccurring in the output data of the specific output buffer andconverting the measured magnitude into a digital code value is performedas follows.

First, a DC component is removed from the high-level output data of thespecific output buffer, and an AC component is extracted as the datanoise at step S22_1. This is in order to acquire only the noiseexcluding the data.

Then, the data noise is amplified, and the magnitude of the amplifieddata noise is quantified by rectifying the amplified data noise at stepS22_2. That is, the magnitude of the amplified data noise is indicatedby a specific analog voltage level.

Then, the quantified magnitude of the amplified data noise is convertedinto the corresponding digital code value at step S22_3. For example,when the voltage level of the quantified data noise is higher than aspecific reference level, the digital code value may be set to reducethe slew rate of the output buffer. On the other hand, when the voltagelevel of the quantified data noise is lower than the specific referencelevel, the digital code value may be set to increase the slew rate ofthe output buffer.

In the step S23 of controlling the slew rates of the plurality of outputbuffers based on the digital code value, when the magnitude of the datanoise is larger than a reference value, the slew rates of the pluralityof output buffers are reduced in response to the digital code value.When the slew rates of the output buffers are reduced, it means that theoutput buffers reduce the amounts of currents driven at the same time.Therefore, the influence of simultaneous switching noise may be reduced,which makes it possible to reduce data noise.

On the other hand, when the magnitude of the data noise is smaller thanthe reference value, the slew rate of the plurality of output buffersmay be increased in response to a corresponding digital code value. Thismeans that simultaneous switching noise does not have an effect on thedata output result. Therefore, the slew rates of the output buffers maybe increased to a proper value for the efficient operation of the outputbuffers.

FIG. 5 is a diagram illustrating the configuration of a semiconductorapparatus implementing the method for reducing output data noiseaccording to an embodiment.

FIG. 5 illustrates output buffers of a data output unit to output datato the outside. However, this technology may be widely applied to anyparts of a semiconductor apparatus using output buffers.

The semiconductor apparatus illustrated in FIG. 5 may include a dataoutput unit 100 and a data noise measuring unit 200.

The data output unit 100 may include an output buffer section 110. Theoutput buffer section 110 may include a plurality of output buffers BUF0to BUFn configured to receive data D<0˜n> and output the received datato input/output pads DQ<0˜n>. At this time, in order to compensate forimpedance mismatching of output data Q<0˜n>, ODT circuits may beconnected to the respective input/output pads DQ<0˜n>.

The respective buffers BUF0 to BUFn of the output buffer section 110drive high data from a power supply voltage VDDQ, and drive low datafrom a ground voltage VSSQ. Since the output buffers BUF0 to BUFnreceive voltages from the common power sources VDDQ and VSSQ,simultaneous switching noises VL1 and VL2 may occur in the groundvoltage VSSQ and the power supply voltage VDDQ due to parasiticcapacitances L1 and L2, respectively, when a plurality of data transitat the same time. The simultaneous switching noises VL1 and VL2 causenoise in the output data Q<0˜n>.

The semiconductor apparatus according to an embodiment measures themagnitude of noise of the output data Q<0˜n> based on the simultaneousswitching noises VL1 and VL2 which may occur to the maximum, andcontrols the slew rates of the output buffers BUF0 to BUFn based on themeasured magnitude of the noise. For example, in order to generate datanoise based on the simultaneous switching noise VL1 of the groundvoltage terminal, low data is driven to a specific output buffer BUFnand data transiting from a high level to a low level are driven to theother output buffers BUF0 to BUFn-1, during the initial setting.Additionally, in order to measure the maximum data noise, low data maybe driven to only the specific output buffer BUFn.

On the other hand, in order to generate data noise based on thesimultaneous switching noise VL2 of the power supply voltage terminal,high data is driven to the specific output buffer BUFn and datatransiting from a low level to a high level are driven to the otheroutput buffers BUF0 to BUFn-1, during the initial setting. Additionally,in order to measure the maximum data noise, high data may be driven toonly the specific output buffer BUFn.

The data noise measuring unit 200 may be configured to measure themagnitude of data noise from the output data Q<n> of the specific outputbuffer BUFn, and generate a slew rate control signal SR<0:m> to controlthe slew rates of the plurality of output buffers BUF0 to BUFn based onthe measurement result. Additionally, it is desirable to control theslew rates of the entire output buffers BUF0 to BUFn together, in termsof design efficiency.

Specifically, the data noise measuring unit 200 may include an ACcomponent extractor 210, an amplifier 220, a rectifier 230, and ananalog-digital converter 240.

The AC component extractor 210 may be configured to remove a DCcomponent from the output data Q<n> of the specific output buffer BUFnand output an AC component as the data noise. This is in order toacquire only the noise excluding data from the output data Q<n>.Specifically, the AC component extractor 210 may include capacitorsconnected in series.

The amplifier 220 may be configured to amplify the to extracted datanoise such that the magnitude of the extracted data noise can berecognized. Specifically, the amplifier 220 may include operationalamplifier (op-amp).

The rectifier 230 may be configured to rectify the amplified data noiseand quantify the magnitude of the amplified data noise. That is, therectifier 230 quantifies the magnitude of the data noise to a specificvoltage level such that the magnitude of the data noise can be compared.Specifically, the rectifier 230 may include rectification capacitorfilters connected in parallel to the capacitors.

The analog-digital converter 240 may be configured to convert thequantified magnitude of the amplified data noise to a correspondingdigital code value and output the digital code value as the slew ratecontrol signal SR<0:m>. Additionally, the analog-digital converter 240may include a register (not illustrated) to store a reference value, andconverts the quantified voltage level of the amplified data noise intothe slew rate control signal SR<0:m> based on the reference value. Forexample, the slew rate control signal SR<0:m> may be set to drop as thequantified voltage level of the amplified data noise is larger than thereference value, and may be set to rise as the quantified voltage levelof the amplified data noise is smaller than the reference value. Sincethe analog-digital converter 240 is generally used in a semiconductorapparatus, the detailed descriptions thereof are omitted herein.

The plurality of output buffers BUF0 to BUFn of the output buffer unit110 receive the slew control signal SR<0:m> to control the slew rates.For example, when the voltage level of the amplified data noise islarger than the reference value, the slew rates may be reduced inresponse to the received slew rate control signal SR<0:m>. When the slewrates of the output buffers BUF0 to BUFn are reduced, it means that theoutput buffers BuF0 to BUFn reduce the amounts of currents driven at thesame time. Therefore, the influence of simultaneous switching noise maybe reduced, and thus data noise may be reduced.

Additionally, when the voltage level of the amplified data noise issmaller than the reference value, the slew rates may be increased inresponse the received slew control signal SR<0:m>. This means that thesimultaneous switching noise does not have an effect on the data outputresult. Therefore, the slew rates of the output buffers may be increasedto a proper reference value for an efficient operation of the outputbuffers BUF0 to BUFn.

FIG. 6 is a circuit diagram illustrating an embodiment of the outputbuffer BUF0 of the output buffer section 110.

The output buffer BUF0 according to an embodiment receives inverteddata/D<0> and transmits output data Q<0>. Specifically, the outputbuffer BUF0 may include a pull-up driver 111 and a pull-down driver 112.

The pull-up driver 111 may be configured to drive high data from thepower supply voltage VDDQ according to the level of the inverteddata/D<0>, and control the slew rate in response to the inverted slewrate control signal/SR<0:m>.

The pull-down driver 112 may be configured to drive low data from theground voltage VSSQ according to the level of the inverted data/D<0>,and control the slew rate in response to the slew rate control signalSR<0:m>.

The pull-up driver 111 may include a plurality of pull-up transistors P1to P4 and a plurality of PMOS switch transistors P5 to P8. The pluralityof pull-up transistors P1 to P4 serve to receive the inverted data/D<0>and output the output data Q<0>. The plurality of PMOS switchtransistors P5 to P8 receives the inverted slew rate controlsignal/SR<0:m> and are then selectively enabled in response to therespective bits of the inverted slew rate control signal/SR<0:m>.

The pull-down driver 112 may include a plurality of pull-downtransistors N1 to N4 and a plurality of NMOS switch transistors N5 toN8. The plurality of pull-down transistors N1 to N4 serve to receive theinverted data/D<0> and output the output data Q<0>. The respective NMOSswitch transistors N5 to N8 receives the slew rate control signalSR<0:m>and are then selectively enable in response to the respectivebits of the slew rate control signal SR<0:m>.

That is, as the number of PMOS and NMOS switch transistors enabledaccording to the slew rate control signal SR<0:m> increases, the slewrate increases. Furthermore, as the number of PMOS and NMOS switchtransistors enabled according to the slew rate control signal SR<0:m>decreases, the slew rate to decreases.

FIGS. 7A and 7B are graphs illustrating an example of the operation ofthe semiconductor apparatus. FIGS. 7A and 7B illustrate the operation ofgenerating the maximum simultaneous switching noise VL1 in the groundterminal and measuring data noise.

FIG. 7A illustrates the operation of the output buffer section 110 ofthe data output unit 100.

Referring to FIG. 7A, during initial setting, low data Q<n> is driven toa specific output buffer, and data Q<0˜n−1> transiting from a high level(i.e., VOH) to a low level (i.e., VOL) are driven to the other outputbuffers in order to generate the maximum data noise in the low dataQ<n>. Due to the influence of the transiting data Q<0˜n−1>, simultaneousswitching noise VL1 occurs in the ground voltage terminal, therebycausing data noise in the low data Q<n>. FIG. 7A also illustrates powersupply voltage VDDQ and ground voltage VSSQ.

FIG. 7B illustrates the operation of the data noise measuring unit 200to receive the low data.

The AC component extractor 210A removes a data component of the low dataQ<n>, and extracts only a noise component as data noise A (see also FIG.5). The amplifier 220 amplifies the data noise A and outputs theamplified data noise B (see also FIG. 5). The rectifier 230 rectifiesthe amplified data noise B, and outputs the magnitude of the amplifieddata noise as a specific voltage level C (see also FIG. 5).

Then, the analog-digital converter 240 converts the voltage level C intoa corresponding digital code value and outputs the corresponding digitalcode value as the slew rate control signal SR<0:m>, and the outputbuffer section 110 controls a slew rate in response to the slew ratecontrol signal SR<0:m>. FIG. 7B also illustrates ground voltage VSSQ.

FIGS. 8A and 8B are graphs illustrating another example of the operationof the semiconductor apparatus. FIGS. 8A and 8B illustrate the operationof generating the maximum simultaneous switching noise VL2 in the powersupply voltage terminal and measuring data noise.

FIG. 8A illustrates the operation of the output buffer section 110 ofthe data output unit 100.

Referring to FIG. 8A, during initial setting, high data Q<n> is drivento a specific output buffer, and data Q<0˜n−1> transiting from a lowlevel (i.e., VOL) to a high level (i.e., VOH) are driven to the otheroutput buffers in order to generate the maximum data noise in the highdata Q<n>. Due to the influence of the transiting data Q<0˜n−1>, thesimultaneous switching noise VL2 occurs in the power supply voltageterminal, thereby causing data noise in the high data Q<n>. FIG. 8A alsoillustrates power supply voltage VDDQ and ground voltage VSSQ.

FIG. 8B illustrates the operation of the data noise measuring unit 200to receive the high data.

The AC component extractor 210A removes a data to component of the highdata Q<n>, and extracts only a noise component as data noise A (see alsoFIG. 5). The amplifier 220 amplifies the data noise A, and outputs theamplified data noise B (see also FIG. 5). The rectifier 230 rectifiesthe amplified data noise B, and outputs the magnitude of the amplifieddata noise B as a specific voltage level C (see also FIG. 5).

Then, the analog digital converter 240 converts the voltage level C intoa corresponding digital code value and outputs the corresponding digitalcode value as the slew rate control signal SR<0:m>, and the outputbuffer section 110 controls a slew rate in response to the slew ratecontrol signal SR<0:m>. FIG. 8B also illustrates ground voltage VSSQ.

While various embodiments have been described above, it will beunderstood to those skilled in the art that the embodiments describedare by way of example only. Accordingly, the semiconductor apparatusdescribed herein should not be limited based on the describedembodiments.

What is claimed is:
 1. A semiconductor apparatus comprising: a pluralityof output buffers configured to electrically connect a plurality ofpower sources; and a data noise measuring unit configured to fix anoutput data of a selected output buffer among the plurality of outputbuffers to have a specific level, measure a noise of the output datausing a capacitance and control a slew rate of the plurality of outputbuffers to based on the noise.
 2. The semiconductor apparatus accordingto claim 1, wherein the data noise measuring unit is configured togenerate a slew rate control signal to control the slew rate.
 3. Thesemiconductor apparatus according to claim 2, wherein when the magnitudeof the noise is larger than a reference value, the slew rates of theplurality of output buffers are decreased in response to the slew ratecontrol signal.
 4. The semiconductor apparatus according to claim 2,wherein when the magnitude of the noise is smaller than a referencevalue, the slew rates of the plurality of output buffers are increasedin response to the slew rate control signal.
 5. The semiconductorapparatus according to claim 1, wherein during initial setting, low datais driven to the selected output buffer, and data transiting from a highlevel to a low level are driven to the other output buffers.
 6. Thesemiconductor apparatus according to claim 1, wherein during initialsetting, high data is driven to the selected output buffer, and datatransiting from a low level to a high level are driven to the otheroutput buffers.
 7. The semiconductor apparatus according to claim 1,wherein the data noise measuring unit includes at least one capacitorfor extracting the noise.
 8. The semiconductor apparatus according toclaim 1, wherein the data noise measuring unit comprises: an ACcomponent extractor configured to remove a DC component from the outputdata of the specific output buffer and extracts an AC component as thenoise; an amplifier configured to amplify the magnitude of the extractednoise; a rectifier configured to rectify the amplified noise andquantify the magnitude of the amplified noise; and an analog-digitalconverter configured to convert the quantified magnitude of theamplified noise into the corresponding digital code value and output theslew rate control signal.
 9. The semiconductor apparatus according toclaim 8, wherein the AC component extractor comprises capacitorsconnected in series.
 10. The semiconductor apparatus according to claim8, wherein the rectifier comprises a capacitor filter includingcapacitors connected in parallel.
 11. The semiconductor apparatusaccording to claim 8, wherein the analog-digital converter comprises aregister to store a reference value, and convert the quantifiedmagnitude of the amplified data noise into the digital code value basedon the reference value.
 12. The semiconductor apparatus according toclaim 1, further comprising a plurality of input/output padselectrically connected to the plurality of output buffers, respectively.13. The semiconductor apparatus according to claim 12, furthercomprising a plurality of ODT circuits electrically connected to theplurality of input/output pads, wherein the plurality of ODT circuits isconfigured to compensate for impedance mismatching of the output data.14. The semiconductor apparatus according to claim 1, wherein theplurality of power sources include a power supply voltage and a groundvoltage.
 15. The semiconductor apparatus according to claim 1, whereinthe plurality of output buffers is configured to drive high data from apower supply voltage.
 16. The semiconductor apparatus according to claim1, wherein the plurality of output buffer is configured to drive lowdata from a ground voltage.